This invention relates generally to suspension mountings, and more particularly, to mountings for the steering system of a railway truck.
Mountings with load suspension and vibration-dampening capabilities have been used in the past to improve the steering and ride characteristics of railway trucks. A typical railway truck includes two side frames connecting front and rear wheelsets mounted on axles. The side frames are connected by a cross-member or bolster and provide the railway truck with a stiff structure for mounting a railway car for carrying cargo. An elastomeric mounting, which is a mounting that includes a pad of an elastic material like rubber or another elastomeric material, is typically positioned between an axle bearing adapter and the side frame adjacent to each wheel to support the frame and car on the axle. The elastomeric mountings permit the axles of the railway car to move horizontally with respect to the side frames to allow the axles to turn or follow the rail curvature. Additionally, the elastomeric mountings support vertical static and dynamic loads, such as the weight of the frame and cargo in the car. This type of suspension is typically utilized in, for example, radial self-steering and non-radial railway trucks. By allowing the axles to turn with respect to the railway truck, the elastomeric mountings reduce the friction between the wheels and the rail, thereby improving their life. Additionally, the reduced friction makes the railway truck easier to pull, thereby increasing fuel economy for the train locomotive.
The railway truck may experience ride control problems when using typical elastomeric mountings, however, due to the mountings"" lack of control over lateral horizontal motion independent of longitudinal horizontal motion. For example, lateral motion of the axles with respect, to the side frames can contribute to instability of the railway truck at high speeds, which produces poor ride characteristics. Since the elastomeric pad of a typical elastomeric mounting is generally flat in the horizontal plane, the lateral spring rate typically is about equal to the longitudinal spring rate. As such, it is generally not desirable to increase the lateral spring rate of the flat elastomeric pad, because this will result in the longitudinal spring rate being correspondingly increased, negatively affecting the steering characteristics of the railway truck.
In order to increase the lateral spring rate independent of the longitudinal spring rate, some elastomeric mountings have included alternating layers of elastomeric pads and rigid shims having a V-shaped, or inverted V-shaped, cross-section. The V-shaped cross-section is in a plane parallel to the axles, or perpendicular to the side frames. For instance, one such elastomeric mounting is described in U.S. Pat. No. 3,699,897 to Sherrick, issued Oct. 24, 1972 and assigned to the assignee of the present invention. The V-shaped cross-section provides a laterally-inclined surface that increases the lateral spring rate of the mount, but does not affect the longitudinal spring rate. Also, the V-shape of the rigid shim, for example, serves to contain the lateral movement of the elastomeric pad, reducing the amount of pure shear and increasing lateral compression within the elastomeric pad, thereby increasing the lateral spring rate. Similar mounts have used other curved cross-sectional shapes, as well as flanges, to restrain the lateral motion of the mount.
These solutions have had limited success in increasing the lateral spring rate, however, because the angle of the inclined V-shaped cross-section is limited by the allowed space for the mount. In many cases, elastomeric mountings are required to adapt to, improve or be retrofit into existing railway trucks. As a result, the available space for the mount may be limited to the space occupied by the existing mount. This available space generally cannot be increased, for example, due to railway truck height limitations for going under bridges and through tunnels, and due to coupler height limitations to permit adjacent railway trucks to be coupled together. In many cases, this available space does not allow a sufficiently inclined V-shaped section to provide a desired lateral spring rate. Thus, since the spring rate of the elastomeric pad cannot be increased without unwelcome changes to the longitudinal spring rate, a less than optimal solution is provided by mountings having V-shaped or other curved-shaped cross-sections.
In order to overcome the drawbacks of the prior art, a mount for use between a side frame member and a bearing adapter in the suspension system of a railway truck has been developed that has a dramatically-increased lateral spring rate. In one embodiment, a mount includes a rigid material layer having at least four sections laterally angled between a horizontal axis and a vertical axis, and at least two of the at least four sections being oriented parallel to a different axis than the other two. A first and second elastic material layer are positioned, respectively, between the side frame member and rigid material layer and the rigid material layer and bearing adapter. Also, the first and second elastic material layers each have at least four sections abutting and conforming to the at least four sections of the rigid material layer. Each of the first and second elastic material layers, as well as the rigid material layer, have a thickness and angular orientation selected to result in the lateral horizontal spring rate having a compression component and a shear component, and wherein the compression component is greater than the shear component. Thus, the angled sections cooperate to dramatically increase the horizontal lateral spring rate of the mount without increasing the horizontal longitudinal spring rate, thereby improving the ride characteristics and high speed stability of the railway truck.
The mount may further include a top plate and bottom plate respectively in contact with the first and second elastic material layers for adapting the mount to the side frame member and bearing adapter, respectively. Preferably, the top plate has a bottom surface with at least four sections that correspond with and are parallel to the at least four sections of the rigid material layer. Similarly, the bottom plate preferably has a top surface with at least four sections that correspond with and are parallel to the at least four sections of the rigid material layer. The mount therefore includes internal sections preferably laterally-angled in opposite directions from one section to the next to form a W-shape, or an inverted W-shape, in cross-section. These angled internal surfaces of the top and bottom plate cooperate with the angled sections of the first and second elastic material layers and the rigid material layer to result in a lateral horizontal spring rate greater than a longitudinal horizontal spring rate.
In addition, the first and second elastic material layers may include cut-out portions defining horizontal longitudinally-extending chambers and, separately or in combination, vertically-extending chambers. These chambers formed in the cut-out portions improve the ability to fine tune the spring rates of the mount. Further, these chambers improve the fatigue life of the elastic material in the mount by increasing the bulge area. For purposes of this disclosure, the xe2x80x9cbulge areaxe2x80x9d is defined as the vertical area in which the first elastic layer and the second elastic layer are free to horizontally expand. The chambers provide the mount with a bulge area greater than the combined perimeter vertical area of the first and second layers, defined as the vertical thickness of each layer multiplied by the perimeter length of each layer.